Polyphenylene sulfide resin (hereinafter abbreviated as PPS) is known as a high-melting and heat resistant crystalline resin with excellent fluidity, organic solvent resistance, electrical characteristics, and flame retardance. However, for use as a molding material for such articles as sliding parts and carriages for optical discs, PPS has poor stability in extrusion and injection molding due to the low degree of polymerization reached. Further, since the glass transition temperature of PPS is about 90.degree. C., which is not very high, PPS molded articles undergo a considerable reduction in rigidity at high temperatures. Thermal rigidity of PPS can be improved by compounding with inorganic fillers, such as glass fiber, carbon fiber, talc, and silica, as suggested in U.S. Pat. Nos. 4,737,539 and 4,009,043. However, molded articles obtained from PPS compositions containing these inorganic fillers tend to suffer from deterioration of appearance or warpage.
In order to prevent warpage and to improve hue, U.S. Pat. No. 5,185,392 proposes a polyarylene sulfide composition comprising (A) 100 parts by weight of a polyarylene sulfide, (B) 0.01 to 10 parts by weight of an organic bisphosphite having the formula: ##STR1## wherein R.sub.1 and R.sub.2 each is an alkyl group, an alkyl group having at least one substituent, an aryl group, an aryl group having at least one substituent or an alkoxy group, (C) 0 to 400 parts by weight of an inorganic filler, and (D) 0.01 to 5 parts by weight of at least one alkoxysilane selected from the group consisting of aminoalkoxysilanes, epoxyalkoxysilanes, mercaptoalkoxysilanes, and vinylalkoxysilanes. The molded articles obtained from this composition have poor appearance while having improved flexural strength.
On the other hand, a polyphenylene ether resin (hereinafter abbreviated as PPE) is recognized as an engineering plastic with heat resistance, dimensional stability, non-hygroscopicity, and excellent electrical characteristics. However, PPE has poor moldability due to its low melt-flow characteristics and also has insufficient oil resistance and insufficient impact resistance.
Hence, various polymer blends mainly comprising PPS and PPE have hitherto been proposed in an attempt to provide a molding material in which the above-described drawbacks are compensated for while retaining their own advantages.
For example, blending PPE and PPS to improve moldability of PPE has been suggested as disclosed in JP-B-56-34032 (the term "JP-B" as used herein means an "examined published Japanese patent application"). Such a mere polymer blend, though achieving an improvement in moldability, exhibits poor affinity at the interface between the PPE and the PPS because the two resins are essentially incompatible with each other. As a result, the composition undergoes phase separation (delamination) on molding, failing to provide molded articles having satisfactory mechanical strength.
In order to overcome the above-described problem of incompatibility between PPS and PPE, several proposals have been made to date. For instance, JP-A-1-259060 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") suggests that a combination of (a) carboxylic acid-, hydroxyl- or epoxy-modified PPE obtained by melt-kneading PPE with maleic anhydride, 2-hydroxyethyl acrylate, glycidyl methacrylate, etc. and (b) similarly functionalized PPS provides a resin composition having excellent mechanical strength. None of these proposals, however, results in sufficient compatibility between PPE and PPS to achieve sufficient improvement in impact resistance.